Our Changing Earth

What is a Theory? In science, it’s almost the same as a fact Must be some sort of evidence to support a theory Even with evidence there is still debate about how true it is

Continental Drift Theory Alfred Wegener said the world used to be one large land mass millions of years ago The land was called Pangaea Pangaea kept moving apart a few centimeters each year After millions of years it became the world we see today

Continental Drift Theory Evidence for Continental Drift includes includes includes includes Continental Edges Rock Structures Same Fossils Climate fit like showed seen in evidence from found Mountains with similar features Puzzle Pieces Continental ice sheets On different continents

Plate Tectonics Plate Tectonics – a more advanced theory about how the continents move Explains that there are loose plates in the earth that shift causing: Oceanic Trenches Mountains Volcanoes Earthquakes.

How Do the Plates Move? http://library.thinkquest.org/17457/english.html

So… Continental Drift – theory that says continents drift around on plates Plate Tectonics – theory that explains WHY scientists believe the continental drift theory is true

Now it’s time for a… REVIEW

What is Continental Drift? Theory that says the continents are moving on plates

What is Plate Tectonics? Theory that explains WHY scientists think continental drift occurs It tells us how the earth’s plates move

Divergent Boundaries This is when the plates move apart It happens mostly between oceanic plates The rising magma causes volcanoes and underwater mountains to be formed

Convergent Boundary When the two plates are in the OCEAN they collide and form deep trenches. When the two plates are on the CONTINENTS they collide to form mountains.

Transform (Sliding) Boundaries This is when the plates slide past each other or move horizontally The sliding is what causes earthquakes This type of boundary is found in California